As the article clearly stated, they did leave people a choice. Some of the tube stations have more than a dozen escalators, and only some were changed to stand

As the article clearly stated, they did leave people a choice. Some of the tube stations have more than a dozen escalators, and only some were changed to standing-only. It makes perfect sense to optimize for throughput generally, but leave some lanes for those relatively few people who need/want to walk (TFA also discusses the difference in this willingness for escalators of different lengths).